Boomerang is NOT possible; I included it mostly to see if anyone would find a way thru it that I hadn't foreseen, but it's certainly not intended to be possible in the demo. That said, it's also not the final hope, so you may have to keep looking!
I found the last one, tricky location you've hidden.
Spoilers/walkthrough below
Map guide:
https://docs.google.com/spreadsheets/d/1fyuGficOFgZ4i3K1cFkaVxTfaH6WHe1KuOiUnDyX...
Let me know where I missed anything